Hi friends,
I have a simple power flow case with an infinite bus and 2 transformers (no
load). The transformers have different turns ratios so I’ll get circulating
current and VAr drop in the banks.
#1 Transformer (100MVA)
161:13.8kV, X=0.1pu
#2 Transformer (100MVA)
161:13.14kV, X=0.1pu
The voltage difference is (13.8kV – 13.14kV)/13.8kV = 0.0478 pu which is the
driving voltage for the circulating current. The circulating current will be
0.0478/0.2pu = 0.239pu A. This circulating current will produce a var drop of
Q = (0.239)(0.239) x (0.2) = 0.01144 pu. This is 1.14MVAr.
I ran the attached power flow case and got 1.13MVAR (nice). But, I don’t
understand the big MVAr drops being reported in the branch report (see below).
What is causing those big values?
================================================================================
| Branch Data |
================================================================================
Brnch From To From Bus Injection To Bus Injection Loss (I^2 * Z)
# Bus Bus P (MW) Q (MVAr) P (MW) Q (MVAr) P (MW) Q (MVAr)
----- ----- ----- -------- -------- -------- -------- -------- --------
1 1 2 0.00 23.81 0.00 -23.24 -0.000 0.57
2 1 2 0.00 -22.68 0.00 23.24 -0.000 0.57
-------- --------
Total: 0.000 1.13
I have a second minor question, how do you specify “branch 1” or “branch 2”
when you have 2 branches between 2 buses? Does MATPOWER just take them in
order they show up in the mpc.branch structure (e.g. the 1st occurrence as
“branch 1”)? I did “help idx_brch” but didn’t see anything specifying.
Thank you,
Russ
